Odd issues with `$state` and non-`$state` BigInts

[Ocean-OS]

Describe the bug

When using $stateful BigInts, I've encountered some weird bugs. I've found that there's some issues with these values when they are retrieved in different ways, such as:

• Template effects always seem to work correctly with $state BigInts ([1]), but...
• Using these values as they are (without putting it in an array or calling .toString() on it) results in odd behavior, sometimes it shows an outdated value or a value greater than what it ever has been [1][2]
• Using these values in an array or in a method results in correct behavior (sometimes) [3]

Additionally, the compiler compiles ++ to +=1 (or (foo+=1)-1), and -- to -=1 (or (foo-=1)+1), which can result in some very ugly bugs. [4]

Reproduction

1. REPL
2. REPL
3. REPL
4. REPL

Logs

No response

System Info

N/A

Severity

more than annoyance

[Rich-Harris]

Except for 4, these all appear to work correctly when I run them outside the playground — are you seeing something different? Hoping this is just something to do with serialization in the playground.

The fourth case is a legitimate bug in the transformation by the looks of it.

[Ocean-OS]

Except for 4, these all appear to work correctly when I run them outside the playground — are you seeing something different? Hoping this is just something to do with serialization in the playground.

The fourth case is a legitimate bug in the transformation by the looks of it.

I have only tested these in the playground.

[Rich-Harris]

Looks like they're all fixed by sveltejs/svelte.dev#916